The tipping point came in October when Thatcher infamously refused the European Community's plans for further integration, prompting her longest serving minister Geoffrey Howe to resign.

In particular, many leading Conservatives wanted the United Kingdom to join the Exchange Rate Mechanism (ERM), a move which Thatcher did not favour.

In June 1989, the then-Foreign Secretary Geoffrey Howe and Chancellor of the Exchequer Nigel Lawson forced Thatcher to agree to the "Madrid Conditions", namely that Britain would eventually join the ERM "when the time was right".

Whereas Thatcher had presided over an economic boom at the time of her third general election victory in 1987, by the autumn of 1989 interest rates had to be raised to 15% to cool inflation, which was now pushing 10%.

The introduction of the deeply unpopular Community Charge (which opponents labelled the "poll tax") had been greeted with widespread non-payment and even a riot in Trafalgar Square in March 1990.

In October 1990, Major and the Foreign Secretary, Douglas Hurd, finally obtained agreement from a reluctant Thatcher that Britain should join the ERM.

By late 1990 the economy was in the first stages of recession, leading to inevitable concerns among Conservative MPs that their party might not win the next election, due by summer 1992 at the latest.

In her Party Conference Speech early in that month, Thatcher mocked the Liberal Democrats' new "bird" logo in language lifted from the famous Monty Python "Dead Parrot sketch".

He now wrote a six-page public letter to his local Association chairman, calling for more regard for the wide range of opinions in the party before leaving for a trip to the Middle East.

[3] At the Lord Mayor's Banquet on 12 November,[4] Thatcher dismissed Howe's resignation by employing a cricketing metaphor: I am still at the crease, though the bowling has been pretty hostile of late.

That is my style.The next day, 13 November, Howe made his resignation speech from the backbenches,[5] addressing his dismay at Thatcher's approach and responding to her recent cricketing metaphor by employing one of his own.

Explaining how, in his opinion, her approach made it hard for British ministers to negotiate for Britain's interests in Europe, he declared: It is rather like sending your opening batsmen to the crease only for them to find, the moment the first balls are bowled, that their bats have been broken before the game by the team captain.Howe's dramatic speech received cheers from the opposition benches and reinforced the change in general perception of Thatcher from the "Iron Lady" to a divisive and confrontational figure.

Many speculated that if Thatcher did not achieve outright victory in the first round, she would either be forced to step down (opening up the field to her supporters who had previously been prevented from standing by their personal loyalty) or else might suffer further challenges from heavyweight figures.

Although Heseltine was a serious leadership contender in his own right, many saw him (correctly, as it turned out) as a "stalking horse" like Meyer in 1989, who might weaken Thatcher only to pave the way for victory by a new candidate in a later round.

[9] Hurd and Major pledged their support for Thatcher, as did Cecil Parkinson, Kenneth Baker and ex-Cabinet minister Nicholas Ridley.

Heseltine was also endorsed by a number of senior ex-ministers including: Howe, Lawson, Lord Carrington (who as a peer had no vote), Peter Walker, David Howell, Ian Gilmour, Norman Fowler, Geoffrey Rippon, Jim Prior, Norman St John-Stevas and Paul Channon, but he had less support among younger MPs amongst whom he had done little to canvass support.

Heseltine's supporters, besides being older than those of the other candidates, tended to be pro-Europeans with a few populist backbenchers like David Evans, Tony Marlow and John Wilkinson.

[11] Heseltine, a self-made multi-millionaire, was photographed at his country mansion Thenford House, Northamptonshire, which played poorly when set beside the stress which Major placed on his humble origins in Brixton.

Major was soon seen as having the potential to lead the Conservatives to another consecutive general election victory; especially after he matched Heseltine's pledge to review the poll tax.

[11] Hurd's Eton College education was a disadvantage, twenty-five years after Iain Macleod's allegation of an Etonian "magic circle" conspiracy.

[15] Henry Kissinger rang Downing Street "in a very emotional state" saying her decision to resign was "worse than a death in the family" and, according to notes by Charles Powell, "Gorbachev had sent Shevardnadze [his foreign minister] out of a high level meeting in the Kremlin to telephone him, to find out what on earth was going on and how such a thing could be conceivable.

Following Thatcher's formal resignation as prime minister, Queen Elizabeth II invited Major to form a government the next day.

Major's premiership began well, and he was credited with restoring a consensual style of Cabinet government after the years of forceful leadership under Thatcher.

Many of the Maastricht rebels were Thatcher supporters, and one of them, Teresa Gorman, devoted the opening chapter of her memoir of the incident to an account of the 1990 leadership contest.

The massive Conservative defeat in 1997 at the hands of Tony Blair and New Labour was thus attributable, at least in part, to the perception of internal division over Europe which had first been exposed by the 1990 leadership election.